Simplified particle emitter and method of operating thereof

ABSTRACT

An emitter assembly for emitting a charged particle beam along an optical axis is described. The emitter assembly being housed in a gun chamber and includes an emitter having an emitter tip, wherein the emitter tip is positioned at a first plane perpendicular to the optical axis and wherein the emitter is configured to be biased to a first potential, an extractor having an opening, wherein the opening is positioned at a second plane perpendicular to the optical axis and wherein the extractor is configured to be biased to a second potential, wherein the second plane has a first distance from the first plane of 2.25 mm and above.

FIELD OF THE INVENTION

Embodiments of the invention relate to particle sources for particlebeam systems e.g. electron microscopes. Particularly, they relate tosimplified particle emitters, charged particle beam devices and methodsof operating simplified emitters and charged particle beam devices. Morespecifically, they relate to an emitter assembly for emitting a chargedparticle beam along an optical axis, a gun chamber for a chargedparticle beam device, a charged particle beam device, and a method ofoperating an emitter assembly or a charged particle beam device,respectively.

BACKGROUND OF THE INVENTION

Technologies such as microelectronics, micromechanics and biotechnologyhave created a high demand for structuring and probing specimens withinthe nanometer scale. Micrometer and nanometer scale process control,inspection or structuring, is often done with charged particle beams.Probing or structuring is often performed with charged particle beamswhich are generated and focused in charged particle beam devices.Examples of charged particle beam devices are electron microscopes,electron beam pattern generators, ion microscopes as well as ion beampattern generators.

During manufacturing of semiconductor devices or the like, a pluralityof observation steps and sample modification steps are usuallyconducted. Common systems include an electron beam column forobservation, imaging, testing or inspecting of a specimen and an ionbeam column for patterning of a specimen or material modification.

In light of the increasing desire to improve the resolution of chargedparticle beam devices, devices with high energy charged particle beamsare desired, for example electron beams with 15 keV and above. Thereby,reliable operation at high voltages and simple and robust mechanicaldesign are to be considered. Further, to increase the throughput ofcharged particle beam devices in applications such as microelectronics,micromechanics and biotechnology, high beam currents and arraying ofemitters at a narrow pitch should also be provided.

SUMMARY

In light of the above, an emitter assembly for emitting a chargedparticle beam along an optical axis according to independent claim 1, agun chamber for a charged particle beam device according to independentclaim 9, a charged particle beam device according to claim 13, and amethod of operating an emitter assembly according to independent claim16 are provided.

According to one embodiment, an emitter assembly for emitting a chargedparticle beam along an optical axis is provided. The emitter assemblybeing housed in a gun chamber and includes an emitter having an emittertip, wherein the emitter tip is positioned at a first planeperpendicular to the optical axis and wherein the emitter is configuredto be biased to a first potential, an extractor having an opening,wherein the opening is positioned at a second plane perpendicular to theoptical axis and wherein the extractor is configured to be biased to asecond potential, wherein the second plane has a first distance from thefirst plane of 2.25 mm and above.

According to another embodiment a gun chamber for a charged particlebeam device is provided. The gun chamber includes an emitter assemblyand an electrode having an opening for trespassing of the chargedparticle beam and being configured to be biased to a third potential.The emitter assembly includes an emitter having an emitter tip, whereinthe emitter tip is positioned at a first plane perpendicular to theoptical axis and wherein the emitter is configured to be biased to afirst potential, an extractor having an opening, wherein the opening ispositioned at a second plane perpendicular to the optical axis andwherein the extractor is configured to be biased to a second potential,wherein the second plane has a first distance from the first plane of2.25 mm and above.

According to a yet further embodiment, a charged particle beam device isprovided. The charged particle beam device includes one or more,typically at least two emitter assemblies. Each of the one or moreemitter assemblies includes an emitter having an emitter tip, whereinthe emitter tip is positioned at a first plane perpendicular to theoptical axis and wherein the emitter is configured to be biased to afirst potential, an extractor having an opening, wherein the opening ispositioned at a second plane perpendicular to the optical axis andwherein the extractor is configured to be biased to a second potential,wherein the second plane has a first distance from the first plane of2.25 mm and above. Thereby, each of the emitters is connected to onepower supply for providing the first potential to the one or moreemitters.

According to an even further embodiment, a method of operating anemitter assembly is provided. The method includes emitting a chargedparticle beam along an optical axis, biasing an emitter to a firstpotential, and biasing an extractor to a second potential, wherein thevoltage between the first potential and the second potential is at least15 kV, particularly at least 20 kV.

Further advantages, features, aspects and details that can be combinedwith embodiments described herein are evident from the depending claims,the description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments. The accompanying drawings relate to embodiments of theinvention and are described in the following:

FIG. 1 shows a schematic view of a charged particle beam device with acommon emitter assembly;

FIG. 2A illustrates a common emitter assembly and the method ofoperation thereof;

FIG. 2B illustrates an emitter assembly according to embodimentsdescribed herein and the method of operation thereof;

FIG. 3 shows a schematic view of a charged particle beam device with anemitter assembly according to embodiments described herein;

FIG. 4 shows a schematic view of a yet further charged particle beamdevice according to embodiments described herein utilizing an emitterassembly according to embodiments described herein;

FIG. 5 shows a schematic view of a charged particle beam device with ayet further emitter assembly according to embodiments described herein;

FIG. 6 shows a schematic view of another charged particle beam deviceaccording to embodiments described herein utilizing another emitterassembly according to embodiments described herein;

FIG. 7 shows a schematic view of a multi-beam gun chamber area accordingto embodiments described herein having a plurality of emitter assembliesaccording to embodiments described herein; and

FIG. 8 shows a flow chart illustrating methods of operating emitterassemblies and charged particle beam devices according to embodimentsdescribed herein.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the various embodiments of theinvention, one or more examples of which are illustrated in the figures.Each example is provided by way of explanation of the invention and isnot meant as a limitation of the invention. For example, featuresillustrated or described as part of one embodiment can be used on or inconjunction with other embodiments to yield yet a further embodiment. Itis intended that the present invention includes such modifications andvariations.

Without limiting the scope of protection of the present application, inthe following the charged particle beam device or components thereofwill exemplarily be referred to as a charged particle beam deviceincluding the detection of secondary electrons. The present inventioncan still be applied for apparatuses and components detecting corpusclessuch as secondary and/or backscattered charged particles in the form ofelectrons or ions, photons, X-rays or other signals in order to obtain aspecimen image.

Generally, when referring to corpuscles it is to be understood as alight signal in which the corpuscles are photons as well as particles,in which the corpuscles are ions, atoms, electrons or other particles.

Within the following description of the drawings, the same referencenumbers refer to the same components. Generally, only the differenceswith respect to the individual embodiments are described.

A “specimen” as referred to herein, includes, but is not limited to,semiconductor wafers, semiconductor workpieces, and other workpiecessuch as masks, glass substrates, memory disks or the like.

According to embodiments described herein, a simplified emitter assemblyfor emitting a charged particle beam along the optical axis is provided.For example, a simplified electron emitter, such as the cold fieldemitter or thermal field emitter can be provided. This is particularlyrelevant for applications having a high energy electron beam within thecharged particle beam device. According to the following description,reference is made to electron beam devices. However, it is to beunderstood that corresponding principles can also be applied for othercharged particle beam devices, such as ion microscopes.

According to typical embodiments, the emitter assembly, the gun chamberand the charged particle beam device can be used for field emitters,such as cold field emitters and thermal field emitters, i.e. emittershaving a high brightness, for example above 1×10⁸ A/(cm² sr). Forexample common hairpin cathodes can have a brightness of 5×10⁴ to 5×10⁶A/(cm² sr), Emitter tips of LaB6 could typically have a brightness of afew 1×10⁷ A/(cm²sr), whereas field emitters can have a brightness of1×10⁸ A/(cm²sr) and above or even 1×10⁹ A/(cm²sr) and above.

FIG. 1 shows an electron beam device 1 having a housing 20 and anobjective lens 13. An electron emitter 5 includes an emitter tipopposite to an extraction electrode 12, which is positively biased (forthe example of electrons) to an extraction voltage Vex. In order toprovide the extraction voltage, power supply 6 is connected to theextraction electrode 12. The assembly of the emitter 5 and theextraction electrode is connected with the power supply for providingthe acceleration voltage Vacc, which can typically be connected toground. This is indicated by reference numeral 2. Thus, the accelerationvoltage determines the beam energy of electrons that are travelling inregions of the charged particle beam device 1 that are on groundpotential or when hitting a grounded target. According to some examples,as shown in FIG. 1, the landing energy of electrons emitted by theemitter 5 on the specimen 3 can be defined by biasing the specimen 3.Thereby, the voltage supply 8 can typically be connected to a portion ofthe charged particle beam device which is biased on the accelerationpotential or the acceleration voltage. Thereby, the landing energy ofthe electron beam can be adjusted or determined by the power supply 8.According to yet further options, which can be used for embodiments ofthe invention described herein, the beam energy within the chargedparticle beam device can further be varied, typically increased, byapplying a voltage Vcol to internal beam guiding components 9 in thecharged particle beam device 1. Accordingly, the power supply 10 can beconnected to ground and the beam guiding components 9.

According to typical examples, the emitter is biased to the accelerationpotential provided by the power supply 4. Thereby, the power supply 4can be connected to ground (reference numeral 2) and the high-voltage isprovided into the chamber 20 through the high-voltage feedthrough 23. Afurther high-voltage, which is provided by the acceleration voltage andthe extraction voltage, i.e. by the power supply 4 and the power supply6, is fed in the chamber through high-voltage feedthrough 24, in orderto connect the extraction electrode 12 with the respective conductor.Further, the voltage feedthrough 32 is provided in order to connect thebeam guiding components 9 with the potential provided by the powersupply 10.

Due to the acceleration voltage and the extraction voltage, an electronbeam is emitted by the emitter 5 and guided along the optical axiswithin the charged particle beam device 1. The charged particle beam canthen be focused by condenser lens 11 and objective lens 13 to be focusedon the specimen 3. Typically, the objective lens 13 includes upper andlower pole pieces 26 and a coil 24. The energy of the electron beam onthe specimen 3 can be adjusted by the power supply 8, which can adjustor provide the landing energy since the power supply 8 is connected tothe acceleration voltage Vacc and defines the potential differencebetween the emitter tip 5 and the specimen 3. On impingement of theprimary electron beam, which is emitted from the emitter, secondaryand/or backscattered particles are generated which can be detected withdetector 15. In order to provide an image of a region of the specimen,scanning devices (not shown in FIG. 1) can be provided to scan theelectron beam over the desired region of the specimen.

Common emitter assemblies follow the emitter manufacturer'srecommendations and datasheets and attempt to maintain the voltagebetween the emitter tip and the extraction potential constant as well asthe tip to extractor at a constant distance. This is generally doneindependent of the acceleration voltage Vacc, which may vary betweensome ten kV to some hundred kV. Thereby, two different designs aremostly used. First, the tip is carried by an elongated emitterinsulator. The emitter insulator is a high-voltage feedthrough capableof withstanding the required acceleration voltage and is also used forsupplying the high voltage to the emitter tip. The extractor is carriedby a different extractor insulator, which is attached to the vacuumchamber, for example a grounded vacuum chamber. Thereby, the extractorvoltage is fed through an additional high-voltage feedthrough capable ofwithstanding essentially the same acceleration voltage, i.e. theacceleration voltage minus the extraction voltage. Secondly, theapproach of the mini module can be used. Thereby, the extractor ismechanically fixed to the structure carrying the emitter. Accordingly,the extractor insulator needs to withstand the comparably smallextraction voltage Vex. However, the additional extraction voltage needsto be fed through the same emitter insulator, which may result inarcing. This mini module design needs only one high-voltage feedthrough.If the mini module itself is well aligned internally, the emitter andthe extractor electric electrode can be aligned together with respect tothe following electrode, such as an anode.

Both designs can also be described with respect to FIG. 2A. In FIG. 2Athe acceleration voltage is provided to the tip of the emitter 5 by thepower supply 4. The power supply 7 provides a suppressor voltage to thesuppressor electrode 22 and the power supply 6 provides the extractionvoltage to the extraction electrode 12. The further electrode 9 can, forexample, be set on ground potential or to another potential of a few kV.For example, the further electrode 9 can be an anode, a first electrodeof a condenser lens, an electrode of a beam guiding component forguiding the beam on a higher potential through the column, or the like.

According to typical optional modification, the suppressor can forexample be in a range of −100 V to −500 V as compared to the emittertip. Thereby, the suppressor is used to suppress thermal emission of theemitter tip.

In the case of the two above-described designs, the tip can, forexample, be on −30 kV the suppressor can be on −30.3 kV, the extractionelectrode 12 can be on −22 kV and the further electrode 9 can be onground. Thus, a large potential difference is created between theextractor aperture and the first electrode. This voltage drop creates aparasitic lens, which is difficult to control because usually there areno alignment elements. Typically, the tip should be close to thecondenser lens, which results in the lack of space for alignmentelements, and additional elements would make it even more difficult toreliably withstand large voltage drops across the gap. Further, if thevoltage drop between the extractor and ground will be several ten kV,such as 22 kV according to the above example, the corresponding fieldwill produce a strong ‘parasitic’ lens and provide many opportunitiesfor high voltage flashover. This can be avoided by the simplifiedemitter assembly according to embodiments described below. Accordingly,even if the tip of emitter 5 can be aligned with respect to theextractor the lens, a parasitic lens between the extractor electrode 12and the further electrode 9, can often not be aligned. Further, thisdesign requires two or more high-voltage feedthroughs. For the minimodule design, it would be possible to align the emitter 5 together withthe extraction electrode 12 with respect to the further electrode 9.However, this does require a very good alignment between the emitter 5and the extraction electrode 12 and still generates strong lens betweenthe extraction electrode 12 and the further electrode 9.

The new concept, according to embodiments described herein, overcomes atechnical prejudice such that it is not necessary and not even advisableto operate an emitter according to the mechanical setup used by theemitter vendors, which is used to qualify the emitter performance andthe production of data sheets. The principal set up is shown in FIG. 2B.In FIG. 2B the acceleration voltage is provided to the tip of theemitter 5 by the power supply 4. The power supply 7 provides asuppressor voltage to the suppressor electrode 22. The extractionelectrode 112 is at a low voltage, which can be similar or close to thevoltage of the further electrode 9. Thus, a power supply 106 can providea relatively small control voltage for the extraction electrode 112. Thefurther electrode 9 for example, can be set on ground potential or toanother potential of a few kV. According to typical embodiments, whichcan be combined with other embodiments described herein, the furtherelectrode 9 can be an anode, a first electrode of a condenser lens, anelectrode of a beam guiding component for guiding the beam on a higherpotential through the column, or the like.

In the case of the two above-described designs, the tip can, forexample, be on −30 kV and the suppressor can be on −30.3 kV, theextraction electrode 112 can be on −5 kV and the further electrode 9 canbe on ground. Thus, the large potential difference which has beencreated between the extractor aperture and the first electrode (see FIG.2A) is significantly reduced. The resulting parasitic lens is alsoreduced.

Accordingly, the extraction electrode 112 is positioned at a largerdistance from the tip of the emitter 5. According to typical embodimentswhich can be combined with other embodiments described herein, thisdistance can be at least 2.25 mm, at least 2.5 mm, at least 5 mm or evenin the range of 7 mm to 20 mm. Further, the potential of the extractionelectrode 112 can be, e.g. for the example shown in FIG. 2B, in a rangeof ground to about 10 kV, typically it can be 2 kV to 7 kV. Accordingly,the influence of the parasitic lens between the extraction electrode 112and the further electrode 9 can be significantly reduced. As describedherein, the tip-to-extractor spacing can be enlarged as long as theextraction voltage, i.e. the potential difference between the tip of theemitter 5 and the extraction electrode 112 is raised accordingly.Thereby, the field strengths of the electric field at the emitter apexcan be provided as desired, i.e., can be kept essentially constant ascompared to common emitter assembly configurations.

It is to be understood that even though examples of potentials aredescribed herein, embodiments of the invention are also directed toexamples where other potentials are used as long as the relativepotentials of the components, i.e. the potential differences orvoltages, are within the described ranges. For example, the tip of theemitter, the specimen or another component can be on ground and theremaining components can be raised to positive potentials or to anotherpotential, respectively.

Yet according to some embodiments described herein, the beam guidingcomponents in the column can be biased to ground potential. This can bein particular used for high speed scanning and detection, for examplefor electron beam inspection system (EBI). If the column itself is seton ground potential, there is no need to keep elements such aselectrostatic scan deflectors or detection electronics on a floating,high potential, which could result in noise in scanning or detectionsignals from partial discharge. Yet according to other options thecolumn might as well be at high potentials, e.g. for critical dimensionmeasuring applications, where the specimen should be on ground. However,also for such applications, the relative potentials from the tip to theextractor and the extractor to a further electrode can be advantageouslyutilized.

FIG. 3 shows an electron beam device 300 illustrating embodimentsdescribed herein. The electron beam device 300 has a housing 20 and anobjective lens 13. An electron emitter 5 includes an emitter tipopposite to an extraction electrode 112, which is positively biasedcompared to the tip to a voltage for extracting the electrons. However,as compared to FIG. 1, in order to extract the electrons, a comparablesmall voltage is provided by control power supply 106, which isconnected to the extraction electrode 112. The power supply 4 forproviding the acceleration voltage Vacc, which can typically beconnected to ground (reference numeral 2) determines the beam energy ofelectrons that have been travelling in regions of the charged particlebeam device 300 that are on ground potential or when hitting a groundedtarget. According to some embodiments, which can be combined with otherembodiments described herein, as shown in FIG. 3, the landing energy ofelectrons emitted by the emitter 5 on the specimen 3 can be defined bybiasing the specimen 3. Thereby, typically the voltage supply 8 can beconnected to a portion of the charged particle beam device which isbiased on the acceleration potential/voltage. Thereby, the landingenergy of the electron beam can be adjusted or determined by the powersupply 8. According to yet further options, which can be used forembodiments of the invention described herein, the beam energy withinthe charged particle beam device can be varied further, typicallyincreased, by applying a voltage Vcol to internal beam guidingcomponents 9 or a first electrode 9 in the charged particle beam device300. Accordingly, the power supply 10 can be connected to ground and thebeam guiding components 9.

According to typical examples, the emitter is biased to the accelerationpotential provided by the power supply 4. Thereby, the power supply 4can be connected to ground (reference numeral 2) and the high-voltage isprovided into the chamber 20 through the high-voltage feedthrough 23. Afurther high-voltage feedthrough can be avoided. The control voltage ofthe power supply 106, can be fed in the chamber through low-voltagefeedthrough 132, in order to connect the extraction electrode 112 withthe respective conductor. Further, the voltage feedthrough 32 isprovided in order to connect the beam guiding components 9 with thepotential provided by the power supply 10. Thereby, typically highvoltage feedthroughs are configured to withstand voltages of 20 kV andabove, whereas low-voltage feedthroughs are configured for voltages of15 kV or below, even though they can also withstand higher voltages,

Due to the acceleration voltage and the extraction voltage, an electronbeam is emitted by the emitter 5 and guided along the optical axiswithin the charged particle beam device 1. The charged particle beam canthen be focused by condenser lens 11 and objective lens 13 on thespecimen 3. Typically, the objective lens 13 includes upper and lowerpole pieces 26 and a coil 24. The energy of the electron beam on thespecimen 3 can be adjusted by the power supply 8, which can adjust orprovide the landing energy since the power supply 8 is connected to theacceleration voltage Vacc and defines the potential difference betweenthe emitter tip 5 and the specimen 3. On impingement of the primaryelectron beam, which is emitted from the emitter, secondary and/orbackscattered particles are generated which can be detected withdetector 15. In order to provide an image of a region of the specimen,scanning devices (not shown in FIG. 3) can be provided to scan theelectron beam over the desired region of the specimen.

As shown in FIG. 2B and FIG. 3, the voltage between the tip of theemitter 5 and the extraction electrode 112 is raised. Even thoughraising a critical voltage may not be considered one first sight, anincrease of the voltage between the emitter and the extraction electrodecan be beneficial, particularly if the acceleration voltage of theemitter tip is raised and/or if a charged particle beam device with ahigh beam energy inside the column is considered. Thereby, it is to beunderstood that a charged particle beam device with a high chargedparticle beam energy has a significantly higher beam energy withinguiding components of the column as compared to the landing energy ofthe charged particles. For example, the beam energy within the columncan be at least 20 times, or at least 30 times higher compared to thelanding energy of the charged particles.

As shown in FIG. 4, the tip-to-extractor distance can be increased suchthat the voltage between the tip of emitter 5 and the extractionelectrode is increased up to the acceleration voltage, for example 30 kVin the example shown above. Thereby, as shown in FIG. 4, the extractionvoltage and the further electrode 9 or the beam guiding components 9 inthe column can be set to ground potential. Accordingly, the full voltagedrop is between the tip and the extractor. Nevertheless, in light of theincreased distance, the field strengths of the electric field at theemitter apex can be provided as desired. Further, the field strengthsbetween mechanical components of the tip carrier and the extractorcarrier can be reduced by also properly increasing the correspondingdistances. Accordingly, in some embodiments there is no need for ahigh-voltage power supply for the extraction voltage or even for anypower supply for the extraction voltage. For example, the firstelectrode of the condenser lens, an anode or the like, can be consideredas the extractor for the emitter. Thus, in the example shown in FIG. 4,the extraction electrode could also be omitted by positioning theguiding components 9 at the position of the extraction electrode 112.Nevertheless, even if internal column components such as an anode, afirst electrode of a condenser lens, or beam guiding components forproviding high energy beams within the column are raised to Vcol, theparasitic lens can be reduced. Further, if no separate isolatedextractor electrode and no Vex power supply are provided, the emissionfrom the tip can be simply controlled by Vacc and/or thetip-to-extractor distance.

Since an omission of a power supply for the extraction electrode mightresult in loss of flexibility of control parameters during operation ofthe electron beam device, the extraction electrode might be movablealong the optical axis as indicated by arrow 113 in FIG. 4. However,even though an emitter is usually operated at nearly the same operatingconditions over its entire lifetime, minor changes in the extractionvoltage, i.e. the voltage between the emitter tip and the extractionelectrode can be necessary to compensate for aging effects. Thesechanges are usually less than 10% to 15% of the extraction voltage. Thiscan be compensated by adjusting the tip to extraction electrode distanceand/or by providing a relatively small voltage, such as the controlvoltage provided by power supply 106 in FIG. 3. Within FIG. 3 themovement of the extraction electrode along the optical axis is alsoindicated by reference 113. However, if for example a control voltage isconnected to the extraction electrode 112, the movement, as shown byarrow 113, can be considered optional. According to typical embodiments,if aging effects of the voltage between the emitter tip and thatextraction electrode are to be compensated for, it is sufficient toprovide a voltage of, for example, 1 kV to 6 kV, such as 3 kV to 4.5 kVto the extractor electrode. According to typical embodiments, which canbe combined with other embodiments described herein, the control voltagesupply can typically vary the voltage between the tip and the extractorby 10% to 15%. If, for example, this voltage is reference to ground, thenecessary insulator can be relatively simple structure and thefeedthrough can be made reliable and off-the-shelf

According to further embodiments, which can be combined with otherembodiments described herein, the power supply for connecting theextraction voltage can be forced to be unipolar by choosing the tip toextractor spacing, such that the aging effects can be compensated for byusing one polarity of the voltage supply only. According to yet furtheralternative options, aging effects could also be compensated for bystatic adjustment of the position of the extraction electrode along theoptical axis, for example, by using shims during a maintenanceprocedure.

Further embodiments can be described with reference to FIG. 5. Therein,a further electron beam device 300 is described. Similar to FIG. 3, theelectron beam device 300 has a housing 20 and an objective lens 13. Anelectron emitter 5 includes an emitter tip opposite to an extractionelectrode 512, which is positively biased compared to the tip to avoltage for extracting the electrons. A suppressor 22, such as asuppressor cup, is provided for suppressing thermal emission of the tip.Thereby, the tip of the emitter extends above 0 mm to 0.5 mm, e.g. 0.25mm below the opening aperture in the suppressor. The power supply 4 forproviding the acceleration voltage Vacc, which can typically beconnected to ground (reference numeral 2) determines the beam energy ofelectrons that are travelling in regions of the charged particle beamdevice 300 that are on ground potential. The landing energy of electronsemitted by the emitter 5 on the specimen 3 can be defined by biasing thespecimen 3. Thereby, typically the voltage supply 8 can be connected toa portion of the charged particle beam device which is biased on theacceleration potential/voltage. The beam energy within the chargedparticle beam device can be varied further, typically increased, byapplying a voltage Vcol to internal beam guiding components 9 or a firstelectrode 9 in the charged particle beam device 300. The power supply 4can be connected to ground (reference numeral 2) and the high-voltage isprovided into the chamber 20 through the high-voltage feedthrough 23. Afurther high-voltage can be avoided. The control voltage of the powersupply 106 can be fed in the chamber through low-voltage feedthrough132, in order to connect the extraction electrode 112 with therespective conductor. Further, the voltage feedthrough 32 is provided inorder to connect the beam guiding components 9 with the potentialprovided by the power supply 10. Due to the acceleration voltage and theextraction voltage, an electron beam is emitted by the emitter 5 andguided along the optical axis within the charged particle beam device300. The charged particle beam can then be focused by condenser lens 11and objective lens 13 on the specimen 3. Typically, the objective lens13 includes upper and lower pole pieces 26 and a coil 24.

The suppressor is typically biased to about −100 V to about −1 kV withrespect to the emitter tip. The energy of the electron beam on thespecimen 3 can be adjusted by the power supply 8, which can adjust orprovide the landing energy since the power supply 8 is connected to theacceleration voltage Vacc and defines the potential difference betweenthe emitter tip 5 and the specimen 3. On impingement of the primaryelectron beam, which is emitted from the emitter, secondary and/orbackscattered particles are generated which can be detected withdetector 15. In order to provide an image of a region of the specimen,scanning devices (not shown in FIG. 3) can be provided to scan theelectron beam over the desired region of the specimen.

As described above, the extraction electrode is positioned along theoptical axis such that the distance between the emitter tip and theextraction electrode aperture, i.e. the opening in the extractionelectrode, is at least 2.25 mm, at least 4.5 mm, e.g. in the range of 4to 10 mm. The control voltage provided by power supply 106 is such thataging effects of the emitter assembly can be compensated for. Accordingto yet further additional or alternative modification, a compensation ofthe extraction voltage or an adjustment of the field strength at theemitter tip can also be provided by the potential applied to thesuppressor. For example, if the suppressor is typically biased to −300 Vas compared to the tip, which is about the manufacturer recommendation,a higher suppressor voltage such as about −600 V to −800 V as comparedto the tip can be used to compensate for one kV to a few kV of a tip toextractor voltage. Thus, aging effects or fine adjustment of thetip-to-extractor voltage can be conducted by one or more of the elementsselected from the group consisting of: the control voltage or therespective power supply, the suppressor voltage or the respective powersupply, a movement of the tip to vary the extractor-tip-distance, and amovement of the extractor to vary the extractor-tip-distance.

According to yet further additional or alternative modifications ofembodiments of methods and apparatuses described herein, the extractorelectrode can be mechanically and electrically connected to the housingof the gun chamber or the charged particle beam device. Thereby, if, forexample, the housing is grounded, the extractor is grounded as well.Thereby, typically, aging effects of the tip can be compensated for, oradjustment of the field strength at the tip can be provided by adjustingthe voltage of the suppressor. According to typical embodiments a changeof the suppressor potential by about 500 V to 1000 V equals a change ofthe tip-to-extractor voltage of about 20% to 40%. This is independent ofthe acceleration voltage. Thus, if an acceleration voltage of about 10kV would be used for a system with a beam energy in the column of 10keV, an increase of the suppressor voltage of e.g. 700 V wouldcompensate for, e.g., about 3 kV tip-to-extractor voltage, and if anacceleration voltage of about 30 kV would be used for a system with abeam energy in the column of 30 keV, an increase of the suppressorvoltage of e.g. 700 V would compensate for, e.g., about 10 kVtip-to-extractor voltage. Thus, the suppressor voltage is a beneficialcompensation tool, because it can efficiently be used in the same way astip-to-extractor voltages variations, because it compensates for apercentage of the tip-to-extractor voltage.

In light thereof, a combination of a variable tip-to-extractor distance,e.g., by moving the emitter, and of a suppressor voltage variations canprovide a good adjustment. Particularly the option of setting theextractor on the housing potential or the potential of internal beamguiding elements provides for these correction parameters also a furthersimplified design.

According to yet further embodiments, which can be combined with otherembodiments described herein, the above described influence of thesuppressor voltage can also be used for control of the beam current.Since the same current change would be achieved with an essentiallyconstant change of the suppressor voltage independent of the beam energywithin the column, no excessive suppressor voltages would be requiredeven for systems having beam energies in the columns for 25 kV andabove. Yet, on the other hand, a correction of the beam current with thetip-to-extractor voltage would be essentially proportional totip-to-extractor voltage. Thus, for the embodiments having an increasedtip-to-extractor voltage described herein, a current adjustment wouldalso require an increased voltage range for adjustment.

Yet according to some embodiments described herein, which can becombined with other embodiments described herein, an acceleration of theelectrons within the column can be provided to a major part, e.g. atleast 70% or least 80%, between the tip and the extraction electrode.Thus, even for high energy beam devices, which have a high energyelectron beam guiding region and/or which have at least 10 times higherbeam energy in the column compared to the landing energy, anacceleration takes place mainly between the tip and the extractor.Thereby, it should be noted that the earlier the charged particles areaccelerated to the high energy, the more energy broadening effects andaberrations due to electron-electron interaction can be reduced. Sincethe emitted electrons are immediately accelerated to essentially theirmaximum energy across the smallest possible distance, electron-electroninteraction is reduced to the absolute minimum. This reduces energybroadening and limits the increase in virtual source size.

According to yet further embodiments, the following feature can beprovided as an advantageous option for a mechanical design providing asimplification regarding High Voltage stability. The extractor structureor extraction electrode can be shaped like a cup that surrounds theemitter structure. Thereby, the extractor electrode 512 has a portion,which is essentially perpendicular to the optical axis and including theextractor aperture or opening. Further, the extractor electrode 512 hasa rim portion surrounding the optical axis, and particularly a region ofthe emitter tip, which is biased to the high acceleration potential.Thereby, the cup can be shaped to have a sufficient distance to theemitter in order to avoid arcing. If for example the emitter and/or theholding structure of the emitter tip has a small radius of curvature insome region, the cup can be shaped to reduce the risk of arcing in thisregion. If a cup-shaped extractor electrode 512 is provided, the volumeof high field strength is confined to the gap between the extractor cupand the emitter and can be easily controlled by proper shaping andmachining of the parts. The potentially dangerous voltage drop along theemitter insulator is mainly handled by making the insulator sufficientlylong and by proper surface design. Since the extractor cup is basicallyat ground potential, all components of the emitter assembly, allcomponents of a gun chamber, and/or all components of the chargedparticle beam device are outside of the shield region and the vacuumchamber is in an area of low field strength which simplifies themechanical design and reduces the risk of arcing significantly. Thisdesign allows reducing the distance between virtual source and condenserlens. This automatically leads to better optical performance.

According to yet further optional modifications of embodiments describedherein, the extractor electrode or the extractor cup can be mechanicallycentered to the condenser lens. Since the extractor cup is to be biasedto a relatively low potential, i.e. there is a relatively smallervoltage between the housing 20 and the extractor electrode 512, thisalignment can be more easily accomplished. A mechanical x-y-alignment ofthe tip with respect to the extractor allows bringing the beam to theoptical axis of the condenser. This improved mechanical alignment leadsto improved optical performance.

FIG. 6 illustrates a further advantageous modification, which can beprovided in light of the simplified design of the emitter assembly. Ascompared to the embodiments shown in FIGS. 3 to 5, the electron beamdevice 300 shown in FIG. 6 shows the insulator 632 for carrying theextractor 512 and shows the insulator 633 carrying the further electrode9 or the beam guiding components 9. The extractor electrode, theinsulators and the further electrodes are formed to provide twosub-chambers in the gun chamber region. A first connection 644 for avacuum pump and a second connection 642 for a vacuum pump are provided.

Thus, having the emitter tip and the region between the extractor andthe further electrode independent of each other, it is possible toevacuate the region of the emitter 5. This is inter alia more easilypossible since the regions outside the cup are shielded by the potentialof the extractor 512, which can be essentially ground (+− a few kV) oressentially the potential of the housing or the beam guiding components(+− a few kV). Accordingly, the proposed design allows easy adaptationto emitters with special vacuum requirements like a lower total pressure(e.g. in the order of magnitude of 1×10⁻¹¹ mbar), lower partial pressureof critical gases (e.g. in the order of magnitude of 1×10⁻⁹ mbar) oreven higher partial pressure of process gases (e.g. in the order ofmagnitude of 1×10⁻⁶ mbar). In common systems, this would usually requireinserting an additional differentially pumped vacuum area betweencondenser and emitter, accompanied by a significant increase intip-to-condenser distance.

According to the embodiments described herein, the extractor can be usedas the differential pumping aperture and separate the volumes below andabove the extractor cup by introducing an insulating barrier between theextractor cup and the vacuum chamber housing. Since the voltage appliedto the extractor cup is small, there is no risk of arcing.

According to another embodiment, the simplified emitter assembly can beadvantageously used for a charged particle multi-beam device, wherein aplurality of emitter tips is arrayed. FIG. 7 shows a gun region of amulti-beam system. The system 700 includes a housing portion 720 and twoor more high voltage feedthroughs 23 (5 insulating feedthroughs areshown in FIG. 7) for the acceleration voltage provided by power supply4. The acceleration voltage is provided to two or more emitters 5 havingrespective emitter tips. Two or more, i.e. a corresponding number,extractor electrodes 512/712 or extractor cups are provided. Accordingto the example shown in FIG. 7, two or more low-voltage feedthroughs 132can be provided to allow for biasing each of the two or more extractorsto an individual potential. This is indicated by one power supply 706having a corresponding number of outputs (5 in FIG. 7). According toalternatives, each control voltage for an extractor electrode can beprovided by an individual power supply or a smaller number of powersupplies can each provide some of the required potentials. The furtherelectrode, i.e. an electrode in beam travelling direction downstream ofthe extractor is shown in FIG. 7 by reference numeral 9. For example,the further electrode 9 can be an anode, a first electrode of acondenser lens, a beam guiding component for providing high beamenergies, or the like.

As described above a combination of a variable tip-to-extractordistance, e.g., by moving the emitter, and of a suppressor voltagevariations can provide a good adjustment for the beam current and/or agood compensation of tip aging equally usable to a variation of thetip-to-extractor voltage. Particularly the option to set the extractoron the housing potential or the potential of internal beam guidingelements provides for these correction parameters also a furthersimplified design, i.e. the power supply 706, the feedthroughs 132 andthe insulators 632, 732 could be omitted. A control of the individualbeams and/or a compensation of the aging of the emitter could becontrolled by one or, preferably, both of the tip-to-extractor distanceand the suppressor voltage. Thus, a multi-beam device can be providedsuch that equal currents for all emitters can be adjusted and aging ofthe emitters can be compensated. The equal current and the option tocompensated for aging can then be provided with a simplified designallowing for a particularly narrow pitch, e.g. 50 mm or smaller, betweenthe emitters as disclosed herein.

Generally, the simplified emitter assembly according to embodimentsdescribed herein, allows for arraying of many emitters at a narrowpitch, e.g. at a distance of 60 mm or smaller. In light of the reducedpotential of the extractor electrodes or extractor cups, and in light ofthe shielding of the extractor cups, small insulators 632/732 forcarrying the extractor can be provided.

According to yet further modification thereof, the individual extractorcups may be reduced to narrow units. For example, cylindrical cupshaving a first portion including the aperture opening and a secondportion having a cylindrical portion surrounding the optical axis, and aconical transition portion between the first and the second portion canbe reduced in one or both lateral dimensions as long as the firstportion providing the field symmetry is not affected by the reducing thecup dimension in one or two directions, e.g. in the form of slices. Therotational symmetry is only required in the vicinity of the tip. Theoverall shielding function does not ask for symmetry. A shielding in thevolume surrounding the emitter structure could also be provided by acommon shield.

The above mentioned control of emission current by a small extractionvoltage provided by power supply 706, which can, for example, bereferred to ground potential, is beneficial in multi column systems,where the beam currents in the individual columns need to be preciselymatched.

The embodiments described herein, may as well include additionalcomponents (not shown) such as condenser lenses, deflectors of theelectrostatic, magnetic or compound electrostatic-magnetic type, such asWien filters, scanning deflectors of the electrostatic, magnetic orcompound electrostatic-magnetic type, stigmators of the electrostatic,magnetic or compound electrostatic-magnetic type, further lenses of theelectrostatic, magnetic or compound electrostatic-magnetic type, and/orother optical components for influencing and/or correcting the beam ofprimary and/or secondary charged particles, such as deflectors orapertures. Indeed, for illustration purposes, some of those componentsare shown in the figures described herein. It is to be understood thatone or more of such components can also be applied in embodiments of theinvention.

According to embodiments described herein, a simplified emitter assemblywith an emitter having an emitter tip, wherein the emitter tip ispositioned at a first plane perpendicular to the optical axis andwherein the emitter is configured to be biased to a first potential, anextractor having an opening, wherein the opening is positioned at asecond plane perpendicular to the optical axis and wherein the extractoris configured to be biased to a second potential, wherein the secondplane has a first distance from the first plane of 2.25 mm an aboveprovides at least one of the following advantages. It can reduce arcingacross the extractor insulator and/or extractor feedthrough as comparedto the common emitter designs, it can reduce arcing inside the minimodule or the emitter insulator/feedthrough, it can reduce arcingbetween the extractor structure and the vacuum chamber, it can reduceloss in optical performance due to the misalignment of the strongparasitic lens between extractor and the following electrode, such as ananode and/or the first electrode of a condenser, and/or it can reduce oravoid loss in optical performance due to avoidable electron-electroninteraction. Yet, a simple and robust mechanical design which can, forexample, be operated reliably at high column voltage, when the emitterstructure is raised to a high voltage Vacc with respect to thesurrounding column parts (vacuum chamber, liner tubes, insulators,feedthroughs, pumps) can be provided. Further, the number ofhigh-voltage feedthroughs configured for 20 kV and above can be reduce,the number of components exposed to high electrical field strength canbe reduced and/or the emitter brightness can be improved. The emitterbrightness can, for example, be improved by reducing energy broadeningof the beam due to an early acceleration, by reducing broadening of thevirtual source, and/or by reducing aberrations of the gun lens byreducing parasitic lenses, which are difficult to align. The designpractically eliminates the ‘parasitic’ lens between extractor andcondenser. Yet further, it can be possible to improve mechanicalalignment of the emitter components and to reduce the distance of thetip to the first (condenser) lens of the system. Further, as describedabove, arraying of emitters at narrow pitch can be provided more easilyand the possibility to incorporate an additional differential vacuumchamber to improve emission stability and/or emitter lifetime can beprovided more easily. One or more of the above aspects can be utilizedto better enable a high beam current operation. Thereby, in addition tothe arraying options, the throughput of a system can be increased.

As described above, the simplified emitter assemblies described hereinhave an increased tip-to-extractor difference as compared to themechanical setup used by the emitter vendors, which is used to qualifythe emitter performance and the production of data sheets. This isprovided by correspondingly increasing the voltage between the tip andthe extractor, and/or by correspondingly decreasing the voltage betweenthe extractor and the further electrode. An acceleration of theelectrons is conducted in the first region between the tip and theextractor. Thus, according to embodiments of operating an emitterassembly, the following steps shown in FIG. 8 are provided. In step 802a charged particle beam, e.g. an electron beam, is emitted. Therefore,in step 804 an emitter is biasing an emitter to a first potential, anextractor is biased in step 804 to a second potential, wherein thevoltage between the first potential and the second potential is at least15 kV, particularly at least 20 kV. As further optional step 808, afurther electrode having an opening for trespassing of the chargedparticle beam is biased to a third potential, wherein the voltagebetween the second potential and the third potential is 15 kV or below,particularly 10 kV or below. According to typical embodiments, which canbe combined with other embodiments described herein, the voltage of theextractor can typically be 10% to 15% of the acceleration voltage Vacc.

As described above, a plurality of embodiments has been described.Thereby, according to one embodiment, an emitter assembly for emitting acharged particle beam along an optical axis is provided. The emitterassembly being housed in a gun chamber and includes an emitter having anemitter tip, wherein the emitter tip is positioned at a first planeperpendicular to the optical axis and wherein the emitter is configuredto be biased to a first potential, an extractor having an opening,wherein the opening is positioned at a second plane perpendicular to theoptical axis and wherein the extractor is configured to be biased to asecond potential, wherein the second plane has a first distance from thefirst plane of 2.25 mm and above. According to optional modificationsthereof, at least one of the following features can be utilized, whichare of the group consisting of: the assembly can further include anextractor support supporting the extractor, wherein the extractorsupport is connected to the extractor and being connectable to a housingof the gun chamber, particularly wherein the extractor support is aninsulating extractor support configured to prevent arcing only forvoltages of 10 kV and below; for example, the extractor support can beadapted to separate the gun chamber in a first vacuum region and asecond vacuum region; the extractor can have a cup-like shape,particularly wherein the extractor includes a first portion with theopening, which is essentially perpendicular to the optical axis, and asecond portion surrounding the optical axis and being adapted to shieldthe first potential applied to the emitter; the emitter or the extractoris movable such that the first distance can be varied; and the assemblyfurther includes a suppressor configured to be biased to a suppressorpotential, wherein the suppressor potential can be varied.

According to another embodiment a gun chamber for a charged particlebeam device is provided. The gun chamber includes an emitter assemblyand an electrode having an opening for trespassing of the chargedparticle beam and being configured to be biased to a third potential.The emitter assembly includes an emitter having an emitter tip, whereinthe emitter tip is positioned at a first plane perpendicular to theoptical axis and wherein the emitter is configured to be biased to afirst potential, an extractor having an opening, wherein the opening ispositioned at a second plane perpendicular to the optical axis andwherein the extractor is configured to be biased to a second potential,wherein the second plane has a first distance from the first plane of2.25 mm and above. According to optional modifications thereof, at leastone of the following features can be utilized, which are of the groupconsisting of: the gun chamber can include a housing of the gun chamberhaving at least one vacuum connection adapted for connecting a vacuumpump, wherein the extractor support is connected to the extractor andthe housing of the gun chamber; the gun chamber can include a secondvacuum connection adapted for connecting a vacuum pump, wherein thevacuum connection is positioned to evacuate the first vacuum region andthe further vacuum connection is positioned to evacuate the secondvacuum region; and the electrode can be positioned at a second planeperpendicular to the optical axis and wherein the distance between thethird plane and the second plane is smaller than 1.5 times the firstdistance.

According to a yet further embodiment, a charged particle beam device isprovided. The charged particle beam device includes one or more,typically at least two emitter assemblies. Each of the one or moreemitter assemblies includes an emitter having an emitter tip, whereinthe emitter tip is positioned at a first plane perpendicular to theoptical axis and wherein the emitter is configured to be biased to afirst potential, an extractor having an opening, wherein the opening ispositioned at a second plane perpendicular to the optical axis andwherein the extractor is configured to be biased to a second potential,wherein the second plane has a first distance from the first plane of2.25 mm and above. Thereby, each of the emitters of is connected to onepower supply for providing the first potential to the one or moreemitters. According to optional modifications thereof, the one or more,typically tow or more, emitter assemblies can be provided within a gunchamber according to embodiments described herein.

According to an even further embodiment, a method of operating anemitter assembly is provided. The method includes emitting a chargedparticle beam along an optical axis, biasing an emitter to a firstpotential, and biasing an extractor to a second potential, wherein thevoltage between the first potential and the second potential is at least15 kV, particularly at least 20 kV. According to optional modificationsthereof, at least one of the following features can be utilized, whichare of the group consisting of: the method can include biasing anelectrode having an opening for trespassing of the charged particle beamto a third potential, wherein the voltage between the second potentialand the third potential is 15 kV or below, particularly 10 kV or below;the first potential can be shielded by a portion of the extractorsurrounding the optical axis; and the beam current can be varied byvarying the tip-to-suppressor voltage.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. An emitter assembly for emitting a charged particle beam along anoptical axis, the emitter assembly being housed in a gun chamber andcomprising: an emitter having an emitter tip, wherein the emitter tip ispositioned at a first plane perpendicular to the optical axis andwherein the emitter is configured to be biased to a first potential; anextractor having an opening, wherein the opening is positioned at asecond plane perpendicular to the optical axis and wherein the extractoris configured to be biased to a second potential, wherein the secondplane has a first distance from the first plane of 2.25 mm and above. 2.The emitter assembly according to claim 1, further comprising: anextractor support supporting the extractor, wherein the extractorsupport is connected to the extractor and being connectable to a housingof the gun chamber.
 3. The emitter assembly according to claim 2,wherein the extractor support is an insulating extractor supportconfigured to prevent arcing only for voltages of 10 kV and below. 4.The emitter assembly according to claim 2, wherein the extractor supportis adapted to separate the gun chamber in a first vacuum region and asecond vacuum region.
 5. The emitter assembly according to claim 1,wherein the extractor has a cup-like shape.
 6. The emitter assemblyaccording to claim 5, wherein the extractor includes a first portionwith the opening, which is essentially perpendicular to the opticalaxis, and a second portion surrounding the optical axis and beingadapted to shield the first potential applied to the emitter.
 7. Theemitter assembly according to claim 1, wherein the emitter or theextractor is movable such that the first distance can be varied.
 8. Theemitter assembly according to claim 1, further comprising: a suppressorconfigured to be biased to a suppressor potential, wherein thesuppressor potential can be varied.
 9. A gun chamber for a chargedparticle beam device, comprising: an emitter assembly, the emitter beinghoused in the gun chamber and comprising: an emitter having an emittertip, wherein the emitter tip is positioned at a first planeperpendicular to the optical axis and wherein the emitter is configuredto be biased to a first potential; an extractor having an opening,wherein the opening is positioned at a second plane perpendicular to theoptical axis and wherein the extractor is configured to be biased to asecond potential, wherein the second plane has a first distance from thefirst plane of 2.25 mm and above; and the gun chamber further comprises:an electrode having an opening for trespassing of the charged particlebeam and being configured to be biased to a third potential;
 10. The gunchamber according to claim 9, comprising: a housing of the gun chamberhaving at least one vacuum connection adapted for connecting a vacuumpump, wherein the extractor support is connected to the extractor andthe housing of the gun chamber.
 11. The gun chamber according to claim10, further comprising: a second vacuum connection adapted forconnecting a vacuum pump, wherein the vacuum connection is positioned toevacuate the first vacuum region and the further vacuum connection ispositioned to evacuate the second vacuum region.
 12. The gun chamberaccording to claim 9, wherein the electrode is positioned at a secondplane perpendicular to the optical axis and wherein the distance betweenthe third plane and the second plane is smaller than 1.5 times the firstdistance.
 13. The emitter assembly according to claim 1, wherein atleast two of the emitter assemblies are combined to form a chargedparticle beam device.
 14. The emitter assembly according to claim 13,wherein each of the emitters of the at least two emitter assemblies isconnected to one power supply for providing the first potential to theemitters.
 15. The emitter assembly according to claim 13, wherein the atleast two emitter assemblies are provided within a gun chamber, whereinthe gun chamber further comprises an electrode having an opening fortrespassing of the charged particle beam and being configured to bebiased to a third potential.
 16. A method of operating the emitterassembly according to claim 10, wherein the voltage between the firstpotential and the second potential is at least 20 kV.
 17. The methodaccording to claim 16, further comprising: biasing an electrode havingan opening for trespassing of the charged particle beam to a thirdpotential, wherein the voltage between the second potential and thethird potential is 15 kV or below, particularly 10 kV or below.
 18. Themethod according to claim 17, wherein the voltage between the secondpotential and the third potential is 10 kV or below.
 19. The methodaccording to claim 16, wherein the first potential is shielded by aportion of the extractor surrounding the optical axis.